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Birds flock to Fort Clatsop, bucking decline trend

Mandy Holmgren hikes to a bird count location in Lewis & Clark National Historical Park. (Kenneth Cole Schneider)
Thursday, April 4, 2019

Birds at Fort Clatsop are thriving.

In fact, populations of most bird species remained stable or increased during the past decade at Lewis and Clark National Historical Park and San Juan Islands National Historical Park, according to a new study published in the scientific journal Northwest Naturalist.

“This analysis suggests that it’s not just the large wilderness parks that are supporting the birds we enjoy in this region,” said the study’s lead analyst, Ecologist Chris Ray. “Smaller parks and protected areas might also provide important habitats for the birds that breed here.”

The new result follows previous research by the same team of scientists from the National Park Service, the U.S. Geological Survey and the Institute for Bird Populations, which showed that birds also were doing well over the past decade in three large wilderness parks of the Pacific Northwest – Mount Rainier, North Cascades, and Olympic.

The good news comes at a time when populations of many bird species have been in decline across the Pacific Northwest and North America.

In the previous study, the authors suggested that large wilderness parks protect bird populations against many human-related threats and preserve old-growth forest that might buffer some effects of climate change. But the explanation made them wonder whether smaller protected areas like Lewis and Clark National Historical Park – which is surrounded by a mixed-use landscape rather than wilderness – can also safeguard birds from the factors that appear to be hurting populations across the larger region.

Birds in smaller parks adjacent to agricultural and residential areas might face additional pressures that birds in wilderness settings avoid. For example, feral cats – or even well-loved cats that live as pets in homes near protected areas – can be relentless predators. Pesticides sprayed near park boundaries can poison birds and reduce the number of insects available for birds to eat.

Since 2005, Institute for Bird Populations field biologists have been counting birds to track population size for the many species that breed in San Juan Island National Historical Park and Lewis and Clark National Park.

Each spring, Biologist Mandy Holmgren and her crew visit one of the parks (alternating parks between years) and hike to dozens of survey stations where they identify and count every bird they see or hear during a seven-minute observation period. Between 2005 and 2016, Holmgren’s team tallied 7,724 detections of 89 bird species at Lewis and Clark.

“Surveying for birds at Lewis and Clark is always interesting because there’s such a diversity of ecosystems—from estuaries and freshwater wetlands to coastal and upland forests,” Holmgren said. “The different habitats attract a great mix of birds and we often find species in this park that we rarely see in the other areas we survey.”

Bird counts include details like how long it takes each observer to detect each bird, and these details can be used to explain some of the variation in counts across years.

“We used an analysis designed to separate the true population trend from the observed trend,” said Ray, who is with the Institute for Bird Populations. “And it was great to see so many positive trends supported after accounting for things like observer effects and annual variation in climate.”

At Lewis and Clark, populations of only three bird species declined during the decade of the study: olive-sided flycatcher, northern flicker, and Hutton’s vireo. During the same period, 20 bird species increased in population.

The researchers found no evidence that any bird species had declined at San Juan Island National Historical Park.

“This analysis suggests that it’s not just the large wilderness parks that are supporting the birds we enjoy in this region,” Ray said. “Smaller parks and protected areas might also provide important habitats for the birds that breed here.”

Fort Clatsop's population of common yellowthroat increased from 2005 to 2016. (Erin Reading)

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